It is known to fit an indirect ophthalmoscope with a camera for detecting an image of the retina being observed, through a condensing lens, by the user. Such ophthalmoscopes are often used in the instruction of students or to inform patients or their relatives, since the image of the retina being observed by an ophthalmologist using the instrument can be displayed on a separate video display unit in real time. The image can also be recorded for subsequent analysis. It is also envisaged that, with the advent of improved telecommunications systems, a non-specialist could use the ophthalmoscope to provide an image which is transmitted to an specialist at a remote location so that the specialist can examine the eye without visiting the patient.
Typically, an indirect ophthalmoscope is a binocular device having viewing optics which have two central mirrors arranged to direct respective images to the left and right eye of the person using the ophthalmoscope. Conventionally, the camera detects an image reflected from an angled half-silvered mirror disposed immediately in front of the two mirrors. It is common for ophthalmoscopes to include head gear to enable them to be used on the user's heads.
Conventionally, the field of view of the camera, i.e. the area imaged by the camera with the aid of the mirror, is fixed relative to the ophthalmoscope. In practice, however, a user may adjust the attitude of the ophthalmoscope relative to his/her head so that the image seen through the viewing optics does not lie wholly within the field of view of the camera.
This can lead to some confusion since the image displayed or recorded using the camera will not then be the same as that seen by the user.
A known type of camera attachment for an ophthalmoscope, produced by Litechnica, includes a facility for adjusting the field of view of the camera, but this attachment makes the instrument lopsided. In addition, light from the image to be detected is reflected into the camera by means of a mirror which is situated on the opposite side of the viewing optics of the ophthalmoscope. Consequently, the image detected by the camera is not congruent with that seen through the viewing optic.